A conventional machine including a load handling apparatus has a lifting arm assembly coupled at a proximal end thereof to a body of the machine and a loading implement coupled to the lifting arm assembly at a distal end thereof.
The coupling of the lifting arm assembly to the body of the machine is a pivotal coupling such that the loading implement can be raised or lowered with respect to the body of the machine by movement of the lifting arm assembly about the pivotal coupling.
Movement of the lifting arm assembly is typically achieved by the use of a lifting ram pivotally coupled at a first end to the body of the machine and at a second end to the lifting arm assembly.
The working implement is coupled to the lifting arm assembly by a pivotal joint such that the working implement can be moved about the pivotal joint between a crowding and a dumping configuration.
A tilt ram is normally provided to move the working implement between the crowding and dumping configurations. A first end of the tilt ram is coupled to the lifting arm assembly and a second end of the tilt ram is coupled to the working implement.
In order to maintain the working implement in a substantially fixed rotational relationship with respect to the machine body, a compensation system is provided. The compensation system includes a compensation ram which is connected to the lifting arm assembly and machine body in parallel with the lifting ram. Thus, an extension of the lifting ram will cause a corresponding extension of the compensation ram. A first chamber of the compensation ram (on a first side of a piston of the ram) is connected to a first chamber of the tilt ram (on a first side of the piston of the ram) and a second chamber of the compensation ram (on a second side of the piston of the ram) is connected to a second chamber of the tilt ram (on a second side of the piston of the ram), such that movement of the lifting arm assembly with respect to the machine body will cause movement of the working implement with respect to the lifting arm assembly in order to maintain a substantially fixed rotational relationship between the working implement and the machine body.
Hose burst protection systems are commonly used in such machines with a hydraulically operated load handling apparatus to reduce the risk of a failed hydraulic hose causing a loss of hydraulic fluid from the hydraulic circuit which would result in the lifting arm assembly falling or working implement tipping in an uncontrolled, undesired, and potentially dangerous manner.
GB2163126 shows a hose burst protection valve coupled between a tilt ram of a working implement and a compensating cylinder. As the lifting arm is raised fluid is transferred from the tilt cylinder to the compensation cylinder to allow the working implement to rotate and maintain a constant rotational relationship with the vehicle. During this process oil passes through the burst protection system. The hose burst protection valve is configured to be normally shut and only partially opens when the arm is lifted. Because of this, the pressure drop across the hose burst protection system is significant, and as such the fluid being transferred to the compensation cylinder is at relatively low pressure, and therefore is of no assistance in lifting the arm.
There is a desire to increase the maximum mass of the load which such machines can lift whilst maintaining the safe operation of the machine in the event of a hose burst event.